Abstract
Quadratic electro-optic coefficients in single crystal SrTiO3 were measured using a Mach-Zehnder interferometer and employing a special phase-modulation technique to find g11=+0.15 m4/C2, g12=+0.04 m4/C2, and g44=+0.08 m4/C2 at room temperature. This result is discussed in connection with DiDomenico-Wemple's theory of nonlinear optical effects in oxygen-octahedra ferroelectrics and also with the induced SHG effect of the crystal.